1. Field of the Invention
The present invention relates to novel artificial hair used for head decorative articles such as wigs, hair accessories etc. and a bundle of fibers using the same for head decorative articles.
2. Description of the Prior Art
At present, the majority of head decorative articles such as wigs, hair accessories etc. are produced from hair materials such as human hair, yak's hair, or artificial hair made of synthetic fibers, and generally these are curled for use. Curl setting in this case is divided roughly into 2 methods depending on the type and the object of hair materials. One method is the so-called cold permanent setting method by chemicals to fix hair materials in an arbitrary curled shape, and the other method is the heat setting method where hair materials are curled under heating with a heat source for dry heating or wet heating and their shape is fixed by cooling. The cold permanent setting method is a method applied to head decorative articles made of keratinous fibers such as proteinous fibers including human hair and yak's hair, while the heat setting method can be applied not only to head decorative articles made of the proteinous fibers described above but also to head decorative articles made of artificial hair consisting of synthetic fibers.
In the heat setting method described above, the temperature conditions for setting vary depending on the type of the starting materials, and the majority of head decorative articles made of artificial hair consisting of synthetic fibers is thermally set at a temperature in the range of about 70 to 160.degree. C., and in this temperature range, articles made of polyvinyl chloride fibers are thermally set at low temperatures, articles made of polyester fibers are thermally set at high temperatures, and articles made of a large number of other synthetic fibers such as acrylic fibers, polypropylene fibers etc. are thermally set at intermediate temperatures in many cases. If artificial hair made of these synthetic fibers is thermally set at temperatures exceeding the upper limit of these appropriate temperatures, curling due to fiber shrinkage occurs and commodity values are lost. Accordingly, in heat setting of artificial hair consisting of synthetic fibers, the temperature conditions for setting should be controlled carefully. On the other hand, the temperature range for heat setting of human hair as a typical example of proteinous fibers is wider than that of the artificial hair consisting of synthetic fibers described above, and heat setting is conducted usually at 100 to 200.degree. C., and the control of the temperature conditions for setting does not require high accuracy. However, human hair when thermally set has the character of tight or loose curls depending on the temperature for setting, so human hair is set generally at higher temperatures than for the artificial hair consisting of synthetic fibers in order to confer durability on curls.
From the foregoing reasons, in cases where the artificial hair consisting of synthetic fibers thermally set at relatively low temperatures, and proteinous fibers thermally set at relatively high temperatures, are mixed for use, heat setting at lower temperatures results in poor durability of curls because of the poor setting force of the proteinous fibers particularly natural keratinous fibers, whereas heat setting at higher temperatures leads to curling due to shrinkage of the artificial hair consisting of synthetic fibers, thus worsening the appearance of the product to reduce commodity values. Accordingly, the proteinous fibers such as human hair etc. and the artificial hair consisting of synthetic fibers are rarely mixed for use, and these are used separately in many cases to produce head decorative articles.
On the other hand, from the viewpoint of articles, head decorative articles such as wigs, hair accessories etc. particularly for weaving, are subjected to curl setting after attached to the head, and thus heat setting with hair irons is frequently used. Among hair irons, a temperature-controllable iron with a cord is cumbersome to handle, so a stove-type hair iron is used in many cases. The heat source of this stove-type hair iron is a stove, and heat setting in this case utilizes the heat remaining in the hair iron heated in a stove, and after removed from the stove, the temperature of the hair iron drops significantly, so the temperature of the stove should be maintained at high temperatures. Accordingly, the control of the temperature of the hair iron at the time of setting is readily made approximate. As a result, if artificial hair consisting of usual synthetic fibers is used in articles for such use, the synthetic fibers when subjected to heat setting by a hair iron are curled due to shrinkage by the high-temperature hair iron to worsen the appearance of the resulting article. Accordingly, under the present circumstances, the starting materials of head decorative articles like a weaving to be thermally set by a hair iron are limited substantially to natural keratinous fibers such as human hair etc.
However, a supply of natural keratinous fibers such as human hair etc. is limited, and their qualities have been worsened year by year to make their fiber length short, their prices are increasing, and these fibers become difficult to obtain. For example, wigs or hair accessories consisting exclusively of natural keratinous fibers with a hair length exceeding than 16 to 18 inches are becoming expensive for the consumer, so there is demand for a method of obtaining them inexpensively.
To meet the demand, polypropylene fibers, polyvinyl chloride fibers, or polyvinyl alcohol (PVA) fibers with higher thermostability than acrylic fibers would be used as starting materials being capable of setting at high temperatures with a hair iron and being mixed with natural keratinous fibers, but at present, there are no examples in which these synthetic fibers are applied to head decorative articles such as wigs, hair accessories etc. As technology relating to hair materials composed of PVA, e.g. Japanese Patent Laid-Open Patent Publication No. 47263/1991 discloses artificial hair consisting of synthetic fibers prepared by spinning a spinning stock solution consisting of a mixture of PVA and chitosan. In this prior art, the mixture is utilized to improve the water resistance and thermostability of the artificial hair, and it is described that if the solid content of chitosan by weight is less than 5 (that is, the solid content of PVA exceeds 95), water resistance, thermostability, gloss etc. cannot be satisfied, and that if particularly high water resistance is required, water resistance can be improved without adding any cross-linking agent by conducting heating treatment for a prolonged period of time until the fibers turn dark brown. In this case, however, use of expensive chitosan in an amount exceeding the predetermined content and discoloration into dark brown by heating treatment, as described above, are problematic. Further, Japanese Patent Publication Nos. 2775/1970 and 30033/1968 disclose artificial hair using fibers prepared by spinning a spinning stock solution composed of artificial hair materials and PVA, and the improvement of setting properties is referred to as one of the objects therein, but it is described that the section of the resulting fiber is an irregular unsymmetrical section, and the effect of improving setting properties is not clarified. In any of the three inventions described above, artificial hair resembling human hair is obtained by spinning a spinning stock solution consisting of PVA and other polymer components, and it not attempted to improve the thermostability of artificial hair using PVA polymer alone.
A large number of PVA fibers produced at present are generally as thin as 8 denier or less, and usually PVA fibers can be obtained by spinning an aqueous solution of PVA into a solidification solution that is an aqueous solution of conc. Glauber's salt to form fibers, followed by drying, stretching and heating treatment. However, the PVA fibers obtained in this method are cocoon- or horseshoe-shaped in section, and spinning of fibers with 25 denier or more in this method involves slow solidification and difficult production. PVA fibers with a circular section can be produced by spinning an aqueous solution of PVA into a coagulation bath of an aqueous solution of conc. caustic soda or by spinning an aqueous solution of PVA containing a small amount of boric acid into a coagulation bath that is an aqueous alkaline solution of conc. Glauber's salt. Under the present circumstances, however, among fibers obtained in this method, those with a thickness of 25 to 100 denier applicable as artificial hair do not have thermostability so that the fibers cannot be thermally set in the range of 160 to 200.degree. C. used for human hair.